In the opinion of I. Kukuljević-Sakcinski, the Roman settlement of Bolentio, positioned on an important Roman road (Poetovio-Mursa), was situated in present-day Orešac. On the Tabula Peutingeriana this settlement is mentioned as Bolentio, while in another source from the end of the 4th century (Itinerarium Hierosolymitanum) it is called “mutatio Bolenta”. The first find from Orešac dates from as far back as 1913, when bronze fittings of a Roman wagon were discovered. The first archaeological investigations were carried out in the 1980s as a collaborative effort of the Archaeological Museum in Zagreb and the Virovitica Municipal Museum. These investigations yielded the remains of a cemetery and architecture with mosaics. The 2004 and 2006 investigations carried out by the Virovitica Municipal Museum revealed architecture with a hypocaust. In addition to excavations, field surveys were carried out on several occasions, upon which the site was placed under protection.

The site of Luka lies north of Orešac, adjacent to the Brežnica river. The site, which consists of several elevations, is an extension of the previously investigated areas of Bašće, Svetina and Dvorina, which yielded remains from the Roman period. The goal of the test excavations carried out in 1997 by the Institute of Archaeology was to verify information unknown until then about that position, and to attribute the elevations to a specific chronological period. The most significant results were obtained at the positions of Luka II/IIa, where 5 simple inhumation graves laid in two rows were discovered. All the deceased persons were placed into ordinary grave pits in the supine position, with arms crossed on the pelvis or a little lower on the thighs. They were oriented E-W, facing east. The objects discovered with the deceased persons include bronze belt buckles (graves 1 and 5), a strap end (grave 9), a crossbow fibula (grave 5) and coins of Julian the Apostate (grave 3) and Valens (grave 5), which date the investigated part of the cemetery to the second half of the 4th century. Twenty or so metres south-west of the investigated graves, a stone was found in situ – a large sandstone placed on smaller stones which served as its foundation. The find of this stone in the immediate vicinity of the cemetery points to a connection between these two positions.

A sondage excavation was carried out in 2007 around 13 metres south-east of the southernmost grave discovered in 1997 at the position of Luka. No other late antique graves were discovered during this campaign, but only a Late Bronze Age pit immediately below the humus. The pit yielded the remains of a portable stove and potsherds. It is supposed that this stratigraphic picture of the site is due to the levelling of the site by an excavating machine, which was planned and carried out after 1997.

The test trench at the site of Dvorine was excavated on cadastral plot 158 (owned by P. Lukinić). Below two recent layers there was another one into which pits were dug, which, based on the finds of coins, glazed pottery and glass bracelets, were dated to the 4th century. The abundant remains of iron slag, clustering in the south-eastern part of the trench, point to metallurgical activity in this part of the site. As regards stone finds, these include a fragment of a quernstone made of volcanic rock, a stone counter, and whetstones. Other finds include Roman coins, Roman ceramics (terra sigillata of various origin), Pannonische Glanzton Ware, locally produced ware, various types of tableware and kitchenware, numerous bracelets and glass beads, bone counters, bronze fibulae, fragments of glass vessels and other objects.

The results obtained by test investigations have corroborated the importance of this site as a settlement, cemetery and road station, as well as the need to investigate and present it in a systematic way.